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REMOTE Wall Study
In 2002, CCHRC undertook a simple study of the performance of two residential dwellings built with different wall systems. One was a standard wall system with an interior vapor/air barrier and the other was a modified PERSIST wall that has been named "REMOTE" which stands for Residential Exterior Membrane Outside Insulation Technique. This was a short-term data collection period as the buildings were monitored from the first of December 2002 through March of the same year. The results of this short term data collection period can really only be used to predict possible long term performance and should not be construed to imply a thorough evaluation of wall system performance of the building over a substantial period of time.
PERSIST uses an approach in which the roof and walls are sealed with a membrane on the exterior of the sheathing and all the insulation is exterior to that membrane. A second roof is then constructed to provide and overhang and protective roofing material. This study hoped to show that by eliminating the extra expense of a second roof, and instead using a traditional cold roof found in most northern construction, that the principals behind PERSIST would be transferable to residential construction in a cost effective manner.
The study consisted of three main parts: (1) monitoring the moisture performance of the REMOTE wall, (2) estimating the cost premium for the REMOTE wall system compared to a standard wall system in two homes built in Fairbanks by the same builder, and (3) comparing the fuel usage of the REMOTE house to that estimated by AkWarm. The complete final report for this study can be found on the CCHRC website. CCHRC has also produced a DVD that shows the process used in constructing a REMOTE house that is available for $15. The results of this study are summarized in the conclusions below.
In this relatively short study, the REMOTE wall system performed quite well. Even with the addition of insulation in the interior stud cavity, the interior of the sheathing never approached the dew point, the temperature at which condensation might occur. The air tightness of the REMOTE house was about 0.4 ACH50 compared to about 2 ACH50 for the standard house. This means that very little energy is wasted heating infiltration air but, like any tight wall system, requires a good mechanical ventilation system. The air tightness also appeared to slightly increase the effectiveness of the fiberglass batt insulation in the stud cavity from a nominal R-11 to an effective R-13. Moisture probes of areas vulnerable to rainfall using a Delmhorst moisture meter indicated moisture levels well below any level of concern.
The cost of the REMOTE wall system is somewhat higher than the conventional system, but apples-to-apples comparisons are difficult to make. In this study, including labor, we compute the REMOTE wall to cost about $0.85 more per square foot of heated space (including the garage) than the conventional approach. Other estimates, that exclude labor, put the cost premium at about $0.30 per SF of heated space. For a 2,500 SF house, the REMOTE premium would be about $1,500 (assuming the labor costs to equal the materials cost) to $2,125 (based on the $0.85 per SF premium) over the conventional wall system. CCHRC is continuing to research ways to reduce this cost; but this cost seems worth the benefits of a healthy, durable home.
There remain questions about the fuel-usage rates observed in this study. The REMOTE home appears to be using fuel at a rate almost twice what was predicted by the AK Warm analysis (which was very low). This rate is not overly excessive compared to other highly rated homes; but is higher than was expected for such a well built home. Given the insulation values and the air tightness results, this is unlikely to be an envelope issue. The best explanation to-date is that the boiler is oversized and the standby and stack losses are using the extra fuel as compared to the predicted rate.